This study is an open-label, dose-titration study of once-daily dosing of cinacalcet, with up to 4 escalating doses given at approximately 3 week intervals. After an initial standard of care optimization period of 2-9 weeks, subjects will proceed to the cinacalcet dose-titration period. Subjects who experience extended toxicity or study drug related serious adverse events or other related, intolerable adverse events will be down titrated to a lower dose of study medication. After subjects have achieved their own maximum tolerated dose (MTD) and completed the once-daily dosing phase, they will continue the study medication for approximately 3 additional weeks with twice daily dosing at their MTD. At the end of the cinacalcet treatment phase of the study, cinacalcet will be discontinued and standard of care (SOC) medications will be adjusted/restarted on an individualized basis. Subjects will continue in this final SOC safety follow-up period for up to 4 weeks until their SOC medications have been re-equilibrated.